Two positive and two negative point charges of equal magnitude are placed at the vertices of a square as shown. The origin of the axes is at the centre of the square.

The electric potential is zero

A.     at the origin of the axes only.

B.     along both the \(x\)-axis and the \(y\)-axis.

C.     along the \(y\)-axis only.

D. along the \(x\)-axis only.

B

Both A and B were allowed as the wording was slightly ambiguous. The symmetry of the situation as a test charge approaches from infinity should have led the candidates to the correct response of B, though.

The poor results of candidates on questions 24 and 25 indicate that more time needs to be spent on this topic.